In the printing of carton blanks, such as those composed of corrugated paperboard, for example, it is well known to apply ink impressions to the blanks with high speed flexographic rollers, and then to transport such inked carton blanks to the next section of the machine by the use of pull rollers which engage the upper and lower surfaces of the inked blanks. However, as the speeds of such machines have increased, and the quality of the ink impressions has become critical, a serious need has arisen to be able to transport the freshly inked blanks to the adjacent section of the machine without contacting the surface of the blank having the moist ink impression. In efforts to solve this problem, a number of transfer systems have been developed in which vacuum boxes are located between the upper and lower reaches of conveyors. The boxes have vacuum slots which communicate with vacuum apertures in the belts, such that, a partial vacuum pressure is applied to the blanks when the apertures in the belts are aligned with the slots in the vacuum boxes. One such system is described in co-pending application Ser. No. 08/033,097 now U.S. Pat. No. 5,383,392. Such systems are effective in transporting the carton blanks without contacting the inked surface; however, the force applied to the blanks is limited by the size of the apertures in the belts, and such apertures may not be made unduly large or they weaken the strength of the belt. Also, relatively low vacuum pressures are required and this, in turn, required relatively expensive vacuum pumps. Registration correction of the blanks is also made more difficult than if the belts did not require such vacuum apertures as will be further explained hereinafter.
A second type of transfer system, known as an open-flow system, has also been developed in which axial flow fans or blowers are utilized to create very large mass flows of air upwardly through a transfer zone between sections of the machine. Solid conveyor belts are provided in this transfer zone, and the high mass flow of air forces the blanks upwardly against the lower reaches of the conveyor as described in U.S. Pat. No. 5,163,891, or against a plurality of drive rollers as taught in U.S. Pat. No. 5,004,221. These systems eliminate the problems associated with the belt apertures; however, they require very high rates of mass flow which can create problems of excessive dust-flow within the machine, as well as undesirable noise and vibration levels.